Air hammer

ABSTRACT

A reciprocal air hammer to drive and retract stress coining pins, interference fit fasteners in restricted access areas and other friction fit components into and out of operable position. A reciprocally movable inner cylinder acts as a valve to regulate air flow in accordance with the position of the piston oscillating within the inner cylinder. The inner cylinder also reacts to piston movement by impacting against the end of the outer cylinder with a low frequency high output force. The outer cylinder contacts the work part to be driven or retracted and expends this energy in driving or retracting the work part.

nited States Patent Lyon July 15, 1975 [54] AIR HAMMER 3,827,507 8/1974 7 Lance 173 119 [75] Inventor: Barry E. Lyon, Long Beach, Cahf. Primary Examiner james A. pp [73] Assignee: McDonnell Douglas Corporation, Attorney, Agent, or Firm-R0bert 0. Richardson;

Santa Monica, Calif. Walter J. Jason; Donald L. Royer [22] Filed: May 3, 1974 ABSTRACT PP 66,685 A reciprocal air hammer to drive and retract stress coining pins, interference fit fasteners in restricted ac- 52 US. Cl. 173/91; 91 /217; 91/276; 9988 areas and other friction fit Components into and 3 135 out of operable position. A reciprocally movable inner [51] Int 2 325 9 00; 01 15 02; FOIL 17 00 cylinder acts as a valve to regulate air flow in accor- [58] Field 6: Search 173/91, 135, 138, 139; dance with the p o of the Piston Oscillating Within 9 2 7 232 235 321 27 25 the inner cylinder. The inner cylinder also reacts to piston movement by impacting against the end of the [56] References Cited outer cylinder with a low frequency high output force. UNITED STATES PATENTS The outer cylinder contacts the work part to be driven 3 299 968 1/1967 C h 73/138 or retracted and expends this energy in driving or reunmng am 3,456,744 7/1969 Altschuler 173/139 tractmg the work part 3,687,008 8/1972 Densmore 91/235 8 Claims, 7 Drawing Figures w 4 4 s w mm A v. fl a .m. y w m M Mg. 9 M a w :2 w. 8 4. 3 4 3 W 51V a /N WWW 2 l 1. W L a 5 4 w W] M W E D D \k W/ L m j v m i 1 6 j x WM w fl m x 4 1 5W. 5 u AT. 1 x MM H H w D. M g MM/ m PM AIR HAMMER BACKGROUND OF THE PRESENT INVENTION Stress coining is the art of pushing a pin of given diameter through a hole of smaller diameter in a metal workpiece as a means of cold-working the metal to increase its fatigue endurance. This forces expansion of the periphery of the hole which produces a favorable metallurgical reaction to the metal around the hole. Naturally, a force on the pin is required. Although more information on stress coining is not deemed essential to the present invention, such information is available in U.S. Pat. No. 3,434,327 for Stress Coining issuing to E. R. Speakman Mar. 25, I969 and assigned to the present assignee.

The utilization of tapered fasteners in the buildingof modern aircraft is an important contributionset forth in U.S. Pat. No. 3,742,584 for Method of Installing Tapered Fasteners Having a High Percent of Contact Surface which issued July 3, 1973 to Marcoux et al. and also was assigned to the present assignee. A force is needed in using check pins to determine the percent of surface contact of the tapered hole with its corresponding fastener and also in installing the fastener for use and its subsequent removal.

Jack hammers, rivet guns, air hammers and vibrators all provide forces for reacting in cutting, smashing, pressing, pounding, smoothing, and other mechanical operations. Such devices may be electrically powered or pneumatically driven. Those which are pneumatically driven require elaborate valve operation to insure that fluid pressure is released at the proper time when the actuating piston is properly placed in its cylinder. Most of the fluid conduits and valving is such that the piston drives in one direction and is simply cocked in the other. Hence, such a device will drive but not retract a friction fit element and is unidirectional in its operation. A vibrator usually has a high frequency, low output with short rapid strokes and little force or power.

The closest approach to the present invention known to Applicant is a Pneumatic Engine, U.S. Pat. No. 926,260 issuing June 29, 1909 to D. Klein. Here a valve 20 is positioned within a piston 19 within a cylinder 10. This valve controls fluid flow which controls piston movement. However, the work output is the reciprocating projecting stud 52 or rod 54 connected to the piston. An air cushion is provided at each end of the piston stroke so the piston does not strike or damage the cylinder end covers.

SUMMARY OF THE PRESENT INVENTION In accordance with the present invention an air hammer is provided that has a low frequency, high force dual-directional output. It consists of an outer cylinder having a reciprocating inner cylinder with a freefloating piston therein. Both cylinders are capped on their ends and have strategically spaced air inlets and vents. An air source is connected to each end of the outer cylinder and the inner cylinder serves as a valve. Air inlets or ports are so located such that when one of the ports in the inner cylinder aligns with one of the outer cylinder ports, pressurized air is introduced into the inner cylinder behind the piston, driving the piston down the inner cylinder. A vent prevents pressure buildup in front of the moving piston. When the piston impacts against the end of the inner cylinder as it moves in this direction, it causes the inner cylinder valve to move to the opposite end of the outer cylinder to an air flow reverse position. Impact energy beyond that required to move the inner cylinder is the hammer output as the end of the outer cylinder impacts against the fastener or work part with which the air hammer is used. When the inner cylinder has been moved to this position, it directs air to the other end of the piston (the end striking the inner cylinder end) to cause its reverse movement back to its first position. A vent prevents pressure build-up in front of the piston in this direction also. This sequence is repeated as the piston moves the inner cylinder valve which reverses the direction of piston movement after the piston and inner cylinder has struck a blow against the outer cylinder end.

The ends of the outer cylinder serve as hammer heads for driving functions such as positioning frictionfit components, riveting, chipping, hammering, etc. Since the driving force is similar in both directions, a modification of an outer cylinder end can adapt it readily for the removal of a friction-fit fastener as well as for its insertion into an opening. Since the velocity of piston movement builds up with distance, and velocity determines impact power, the longer the outer cylinder the greater will be the impact blow on its end. Since travel of the piston and. inner cylinder is within the confines of the outer cylinder which has minimum movement as it impacts on a work part, this device is very compact and can be used in very confined areas.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing the inner cylinder and piston in a first position,

FIG. 2 is a sectional view showing the inner cylinder in the first position and the piston in a second position impacting the end cap of the inner cylinder,

FIG. 3 is a sectional view showing the inner cylinder in the second position impacting the end of the outer cylinder in response to previous impact by the piston,

FIG. 4 is a sectional view showing the inner cylinder in its second position with the piston en route returning to its first position,

FIG. 5 is a view of the parts in disassembled array,

FIG. 6 is a perspective view of the hammer used in fitting a tapered pin into a tapered hole, and

FIG. 7 is a perspective view of the hammer used in pulling a nail from a board.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT Referring now to FIG. 1 there is shown in section an outer cylindrical tube 10 having threaded end caps 12, 14 at each end. A smaller inner cylindrical tube 16 with threaded end caps 18, 20 is slidable within the outer tube 10. Within the inner tube is a piston 22 adapted to move under pressure fore and aft between the end caps 18, 20 of the tube 16. Piston 22 has truncated conical end surfaces 24, 26 which will permit their abutment against end caps 18, 20 respectively and yet permit pressurized air, or other fluid, to build up behind the piston to move it to the other end of tube 16.

Air inlets 28, 50 are strategically spaced on tube 10 near each end. Tube 16 has air inlets 32, 34 near its ends. When inner tube 16 is positioned against left end cap 12, as shown in FIG. 1, air passes through aligned inlets 28 and 32 into the air space 36 around truncated cone end surface 24. With inner tube 16 in this position, air inlet 50 at the right end of tube 10 is blocked and is inoperative since inlet 34 of inner tube 16 is not aligned with it. Instead, inlet 34 is aligned with a vent 38. This vent is an annular groove on the inner wall of tube 10 which communicates with an opening 40 in tube 10. This vents the air space 42 in front of piston 22 to atmosphere and thus prevents a harmful pressure build-up in front of piston 22 as it moves to the right in the direction of arrow 44. Other vents and openings will be described with reference to other FIGURES where the operation and positioning of the inner tube 16 and piston 10 has changed.

In FIG. 2 the piston 22 has advanced to the right, in the direction of arrow 44 until piston end 26 has made contact with end 20 of tube 16. The momentus of the mass of piston 22 then causes tube 16 to move to the right, also in the direction of arrow 44, until it impacts against end 14. This drives the outer tube 10 to the right, to the position shown in FIG. 3, as the power output of the device. An annular groove 46 on the inner surface of tube 10 just preceding end 14 is connected through vent 48 to atmosphere to avoid a cushioning pressure build-up in front of tube 16 as it moves to the right for impact with outer tube end 14.

As can be seen in FIG. 3, with inner tube 16 moved to the right, air inlet 28 at the left is ineffective but the air inlet 50 in outer tube 10 on the right is in communication with air inlet 34 at the right end of inner tube 16. This permits a build-up of air pressure in tube 16 in the cavity around truncated end 26 of piston 22, forcing it back to the left as shown by arrow 54.

In FIG. 4 the piston 22 has started its return, moving to the left as shown by arrow 52. Since inner tube 16 remains on the right in contact with end 14 of outer tube 10, vent 32 near left end 18 of inner tube 16 is in communication with vent 54 to prevent pressure buildup in front of piston 22 as it moves to the left. An annular groove 56 on the inner surface of outer tube 10 adjacent left end 12 communicates through vent 58 to atmosphere. This prevents pressure build-up which would cushion the impact of end 18 against end 12 when the inner tube 16 has been moved to the left upon impact of piston 22 against inner tube end 18. The next position of the piston 22 and inner tube 16 is that shown in FIG. 1. This completes one cycle of movement. Since the impacts are the same in either direction, the output of this tool may be to drive, as in FIG. 6, or to pull, as in FIG. 7.

FIG. shows the relationship of the parts and the relative positioning of the various inlets. As was previously mentioned, the piston 22 is adapted to move within inner tube 16 which, in turn, is adapted to move within the outer tube 10. Obviously piston 22 is shorter than inner tube 16 which is shorter than outer tube 10. Their diameters are such that friction is low yet air leakage is also minimal.

The spacing is such that when inner tube 16 moves to the left and end 18 abuts the inner surface of end 12, inlet 28 is in communication with opening 32 in inner tube 16. When this occurs, opening 34 in inner tube 16 communicates with vent 40 in outer tube to prevent pressure build-up as piston 22 moves to the right. Also vent 48 is open to prevent pressure build-up when inner tube 16 moves to the right.

Also, the spacing is such that when inner tube 16 moves to the right and end abuts the inner surface of end 14, inlet 50 is in communication with opening 34. When this occurs, opening 32 in inner tube 16 communicates with vent 54 to prevent pressure build-up as piston 22 moves to the left. Also vent 58 is open to prevent pressure build-up when inner tube 16 moves to the left.

As previously stated, the piston in the air hammer reciprocates under equal pressure in inlets 28 and 50, and

accordingly causes the inner tube to strike the two ends of the outer tube with equal force. The overall lengths of the tubes and the inlet pressures determine the output shock force and the frequency of the vibrations. In FIG.- 6 is shown how the air hammer is used in snugly fitting a tapered fastener 60 in a tapered hole 62 in plates 64, 66. If the plates are horizontal the axis of tube 10 is vertical and the whole tool vibrates or oscillates in a vertical direction shown by arrows 68, with hammer end 14 striking pin 60 and driving it in the direction of arrow 72. In this case inputs 28 and 50 at each end of tube 10 is connected by a Tee connection to an air supply, not shown, through connector 76. A valve 78 may be used to reduce the pressure if desired. Another valve 80 may be used to control pressure in inlet 50. By proper adjustment a greater force may be applied downwardly in the direction of arrow 68 with a lesser lifting force applied upwardly in the direction of arrow 70.

In FIG. 7 is shown the air hammer used to remove a nail 82 from a board 84. For this purpose end 12 is adapted with claw cars 86 which fit under the head of nail 82. As the ears 86 are vibrated the head of the nail is moved upward in the direction of arrow 88. The nail may be pulled farther out by resting end 12 on the board 84 and tilting the upper end of the hammer back in the direction of arrow 90. By reducing the pressure at inlet 50 with valve 80, the downward force is lesse'ned, if desired, without reducing the upward force.

It may be noted that the ends of the tubes are threadedly connected to the tubes and may be removed to replace the inner tube and/or piston if desired to change the frequency and force characteristics as desired. In this manner the air hammer may be a high frequency vibrator or a low frequency impactor with relatively high force.

While the air hammer has been described as using a pressurized air supply, it also may be hydraulically actuated. In such event, release vents 40 and 54 preferably may be connected to a low pressure return line to complete the hydraulic system.

While certain exemplary embodiments of this invention have been described above and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of, and not restrictive on, the broad invention and that I do not desire to be limited in my invention to the specific constructions or arrangements shown and described, for various obvious modifications may occur to persons having ordinary skill in the art.

I claim:

1. A fluid powered air hammer comprising:

an outer tube having closed ends,

an inner tube having closed ends,

a piston, and a pressurized fluid source,

said piston being within said inner tube and adapted to oscillate between the ends thereof,

said inner tube being within said outer tube and adapted to oscillate between the ends thereof,

said inner tube comprising valve means between said piston and said pressurized fluid source for supplying pressurized fluid behind alternating ends of said piston to cause said piston to oscillate between said ends of said inner tube.

2. A fluid powered hammer as set forth in claim 1 wherein said piston is free-floating and has truncated conical ends to permit pressurization in said inner tube between said piston and an inner tube end contacted thereby.

3; A fluid powered hammer as set forth in claim 1 wherein the force of said piston in engaging said inner tube causes said inner tube to impinge against an end of said outer tube.

4. A fluid powered hammer as in claim 1 wherein said vaive means diverts fluid from Said fluid source to that end of said piston contacting an end of said inner tube.

5 A fluid powered hammer as set forth in claim 1 wherein one of said outer tube ends serves as a hammer head for engaging and driving an object to be driven thereby.

(it A fluid powered hammer as set forth in claim 1 wherein one of said outer tube ends has claw ears at- 'tached thereto to engage and lift out a fastener from its mounting.

7. A fluid powered hammer as set forth in claim 1 wherein said fluid source is connected to said outer tube near each end thereof, said inner tube conducting fluid from said source to that end of said piston in abutmerit With an end of said inner tube at that point in time during oscillation of said piston.

8. A fluid powered hammer as set forth in claim 1 including a fluid pressure reduction means in between Said fluid source and said valve means for reducing fluid pressure against said piston in one direction to drive said piston with less force in said one direction than in the other direction. 

1. A fluid powered air hammer comprising: an outer tube having closed ends, an inner tube having closed ends, a piston, and a pressurized fluid source, said piston being within said inner tube and adapted to oscillate between the ends thereof, said inner tube being within said outer tube and adapted to oscillate between the ends thereof, said inner tube comprising valve means between said piston and said pressurized fluid source for supplying pressurized fluid behind alternating ends of said piston to cause said piston to oscillate between said ends of said inner tube.
 2. A fluid powered hammer as set forth in claim 1 wherein said piston is free-floating and has truncated conical ends to permit pressurization in said inner tube between said piston and an inner tube end contacted thereby.
 3. A fluid powered hammer as set forth in claim 1 wherein the force of said piston in engaging said inner tube causes said inner tube to impinge against an end of said outer tube.
 4. A fluid powered hammer as in claim 1 wherein said valve means diverts fluid from said fluid source to that end of said piston contacting an end of said inner tube.
 5. A fluid powered hammer as set forth in claim 1 wherein one of said outer tube ends serves as a hammer head for engaging and driving an object to be driven thereby.
 6. A fluid powered hammer as set forth in claim 1 wherein one of said outer tube ends has claw ears attached thereto to enGage and lift out a fastener from its mounting.
 7. A fluid powered hammer as set forth in claim 1 wherein said fluid source is connected to said outer tube near each end thereof, said inner tube conducting fluid from said source to that end of said piston in abutment with an end of said inner tube at that point in time during oscillation of said piston.
 8. A fluid powered hammer as set forth in claim 1 including a fluid pressure reduction means in between said fluid source and said valve means for reducing fluid pressure against said piston in one direction to drive said piston with less force in said one direction than in the other direction. 